The need for cleaner burning fuels has resulted in a continuing world-wide effort to reduce sulfur levels in hydrocarbon streams such as gasoline and diesel fuels. The reduction of sulfur in such hydrocarbon streams is considered to be a means for improving air quality because of the negative impact the sulfur has on performance of sulfur sensitive items such as automotive catalytic converters. The presence of oxides of sulfur in automotive engine exhaust inhibits and may irreversibly poison noble metal catalysts in the converter. Emissions from an inefficient or poisoned converter contain levels of non-combusted, non-methane hydrocarbons, oxides of nitrogen, and carbon monoxide. Such emissions are catalyzed by sunlight to form ground level ozone, more commonly referred to as smog.
Thermally processed gasolines such as, for example, thermally cracked gasoline, visbreaker gasoline, coker gasoline and catalytically cracked gasoline (hereinafter collectively referred to as “cracked gasoline”) contain, in part, olefins, aromatics, sulfur, and sulfur containing compounds. Since most gasolines, such as, automobile gasolines, racing gasolines, aviation gasolines, boat gasolines, and the like contain a blend of, at least in part, cracked gasoline, reduction of sulfur in cracked gasoline will inherently serve to reduce the sulfur levels in most gasolines, such as, for example, automobile gasolines, racing gasolines, aviation gasolines, boat gasolines, and the like.
The public discussion about gasoline sulfur has not centered on whether or not sulfur levels should be reduced. A consensus has emerged that lower sulfur gasoline reduces automotive emissions and improves air quality. Thus, the rules to date have focused on the required level of reduction, the geographical areas in need of lower sulfur gasoline, and the time frame for implementation.
As the concern over the impact of automotive air pollution continues, it is clear that further effort to reduce the sulfur level in automotive fuels will be required. While the current gasoline products contain about 330 parts per million (ppm) sulfur, the US Environmental Protection Agency recently issued regulations requiring the average sulfur content in gasoline to be less than 30 ppm average with an 80 ppm cap. By 2006, the standards will effectively require every blend of gasoline sold in the United States to meet the 30 ppm level.
In addition to the need to be able to produce low sulfur content automotive fuels, there is also a need for a process which will have a minimal effect on the olefin content of such fuels so as to maintain the octane number (both research and motor octane number). Such a process would be desirable since saturation of olefins greatly affects the octane number. Such adverse effect on the olefin content is generally due to the severe conditions normally employed, such as during hydrodesulfurization, to remove thiophenic compounds (such as, for example, thiophenes, benzothiophenes, alkyl thiophenes, alkylbenzothiophenes, alkyl dibenzothiophenes and the like) which are some of the most difficult sulfur containing compounds to remove from cracked gasoline. In addition, there is a need to avoid a system wherein the conditions are such that the aromatic content of the cracked gasoline is lost through saturation. Thus, there is a need for a process which achieves desulfurization and maintains the octane number.
In addition to the need for removal of sulfur from cracked gasolines, there is a need for the petroleum industry to reduce the sulfur content in diesel fuels. In removing sulfur from diesel fuels by hydrodesulfurization, the cetane is improved but there is a large cost in hydrogen consumption. Such hydrogen is consumed by both hydrodesulfurization and aromatic hydrogenation reaction.
Thus, there is a need for a desulfurization process without a significant consumption of hydrogen so as to provide a more economical process for the treatment of cracked gasolines and diesel fuels.
As a result of the lack of success in providing a successful and economically feasible process for the reduction of sulfur levels in cracked gasolines and diesel fuels, it is apparent that there is a need for a better process for the desulfurization of such hydrocarbon streams which has minimal effect on octane levels while achieving high levels of sulfur removal.
Traditionally, compositions used in processes for the removal of sulfur from hydrocarbon streams have been agglomerates used in fixed bed applications. Because of the various process advantages of fluidized beds, hydrocarbon streams are sometimes processed in fluidized bed reactors. Fluidized bed reactors have advantages over fixed bed reactors, such as, for example, better heat transfer and better pressure drop. Fluidized bed reactors generally use reactants that are particulate. The size of these particulates is generally in the range of from about 1 micron to about 1000 microns. However, the reactants used generally do not have sufficient attrition resistance for all applications. Consequently, finding a composition with sufficient attrition resistance that removes sulfur from these hydrocarbon streams and that can be used in fluidized, transport, moving, or fixed bed reactors is desirable and would be a significant contribution to the art and to the economy.